1. Field of the Invention
This invention relates to a lead cartridge opening and closing unit in cassette type mechanical pencils.
2. Description of the Prior Art
Recently, a so-called cassette type mechanical pencil was developed by means of which the lead members used can be exchanged and/or supplied by, for example, exchanging a whole cartridge 101 thereof in which writing lead members are contained as shown in FIG. 1. Such exchange may be accomplished without refilling such lead members one by one so that staining of a user's hands by a lead member is avoided.
In such a conventional cassette type mechanical pencil, the lead cartridge 101 is simply provided with a cap 102 at the extreme end thereof. In this connection, exchange and/or supply of lead members for a mechanical pencil has been conducted in such a manner that the end cap 102 is first removed from the cartridge to throw away the cap, and the extreme end of the lead cartridge is fitted in an outer cylinder 103 of the mechanical pencil in its open state as shown in FIG. 2.
Accordingly, there has been such a problem that when the lead cartridge is inclined in even a slight degree after removing the end cap 102, the lead members 104 move out of the lead cartridge 101 and they fall off the lead cartridge.
As a result, it is necessary to insert the lead cartridge 101 into the outer cylinder 103 while always maintaining the lead cartridge 101 in an upward orientation.
Furthermore, in the case where the lead cartridge 101 is released from the outer cylinder 103, there has been also such a problem that when the lead members 104 are inclined downwardly in even a slight degree, the lead members 104 move out of the lead cartridge so that they remain in the outer cylinder 103.
Moreover, a conventional cassette type mechanical pencil has such a construction that the lead cartridge 101 containing a number of lead members 104 is contained in the outer cylinder 103 together with a lead guide 105 for detachably inserting the lead cartridge 101 thereinto as shown in FIG. 2. In such construction as described above, provision of a tapered beveled portion 107 is required on the inner surface of the extreme end of the lead cartridge 101 for capturing remaining lead members in the outer cylinder 103. In addition, the inner wall of the outer cylinder 103 is required to form into an inside protuberant wall portion 106 different in level from the inner wall of the outer cylinder 103 as shown in FIG. 2. For this reason, there has been a problem in that the diameter of the lead cartridge is restricted because of the existence of the inside protuberant wall portion 106, so that capacity for containing lead members decreases. in these circumstances, since application of extrusion molding to the outer cylinder 103 provided with the protuberant wall portion 106 as mentioned above is impossible, injection molding must be applied in this case where the metallic mold for the latter molding operation becomes more expensive than that of the former molding procedure and this also results in another problem.
In this respect, the present applicant has attained the elimination of the above described problems by means of the opening and closing unit for the lead cartridge disclosed in Japanese Patent Publication No. 204692/1986 which was previously filed by the present applicant.
In the opening and closing unit for the lead cartridge according to the above identified prior application, a forwardly and extensively protruded chuck type opening and closing unit from the extreme end of its lead cartridge has been described. However, such forward and extensive protrusion of the chuck type opening and closing mechanism as described above makes the appearance thereof unfavorable. Moreover, there has been still a problem in that the whole length of the lead cartridge becomes longer by the protruded length of the above described chuck type opening and closing mechanism, whereby the whole shaft length of a mechanical pencil to which said lead cartridge is applied becomes longer.